It is desirable to monitor tires for parameters such as temperature and pressure. It is particularly advantageous to monitor large tires for off-the-road (OTR) vehicles since these tires are very expensive and must be regularly maintained to maximize vehicle and tire efficiency.
In the past, tire monitoring devices have ranged from systems that monitor tire pressure by connections to the valve stem (U.S. Pat. No. 4,734,674), to systems that use magnetic coupling to receive the signals external of the tire (U.S. Pat. No. 4,588,978), to sophisticated systems that measure rate of change of pressure in the tire and then change the rate of transmission of the data depending upon the rate of change of pressure (U.S. Pat. No. 5,656,992). Other systems are activated by a radio frequency transmission that energizes the tire tag circuit by inductive coupling devices. See U.S. Pat. No. 5,166,676.
Passive devices that rely on inductive magnetic coupling or capacitive coupling generally have the disadvantage of requiring lengthy coil windings, thus requiring major modifications in the tire construction and assembly process. Another serious disadvantage with such passive devices is that the interrogator must be positioned in very close proximity to the tire, usually within a few inches of the tire, in order to allow communication between the tire and the device. Because of the proximity requirements, continuous monitoring is impractical since it would essentially require that an interrogator be mounted at each wheel of the vehicle. Manual acquisition of the data from the passive devices embedded in each of the tires is also cumbersome and time-consuming because of the proximity requirements.
Other prior art devices used for monitoring tire conditions are comprised of self-powered circuits that are positioned external of the tire, such as at the valve stem. Externally mounted devices have the disadvantage of being exposed to damage such as from weather and vandalism. Additionally, externally installed devices can easily become disassociated from a particular tire that is being monitored.
Another disadvantage with known tire monitoring and identification devices is that communication transmissions are achieved using conventional radio frequencies that generally require a relatively large antenna which must be mounted externally or secured to the tire in such a manner that relatively major modifications are required in the tire construction or assembly process.
Various ones of these problems have been addressed by the devices shown and described in U.S. Pat. Nos. 5,500,065; 5,562,787; 5,573,610; and 5,573,611. However, these devices are contained within the tire wheel chamber and have difficulty transmitting data through the tire to external receivers. Also some additional devices are contained within valve stems that do not attached directly to the tire so they do not provide a permanent record of the tire since a different tire could be removed and replaced with another tire on the same rim containing the device. Also, these prior art devices either attach to the tire, to the wheel, or to the valve stem exclusively and do not provide design flexibility which is desired in many applications.
Also, when using RF frequency communication, difficulties are encountered in transmitting the signals to a remote location due to the signals being required to pass through the tire sidewall(s), which, due to tire thickness at this location, materially reduces the transmission efficiency thereof. It has been observed that the amount of carbon content in the tire affects transmissibility of RF signals thus posing problems for antenna designs. Further, problems occur with prior art antennae etched into or placed on a substrate or printed circuit board. Good transmissions from such construction may occur in one direction only through the tire sidewalls. A tire may be “reverse” mounted with the tag on an inside wall. Such mounting may increase the difficulty of transmitting through the tire sidewalls in the desired direction. It would be desirable to have an antenna structure that can transmit in at least two directions through both sidewalls.
Although the tire monitoring devices disclosed in the above-mentioned documents provide limited advantages, a tire monitoring system is needed that provides versatility and flexibility by permitting separation of system functions into discrete components capable of improving external RF communication reception in terms of signal/noise ratio, reproducibility and distance. Separate components are used, but combined into a single device structure, including a measuring device attached directly to the tire inner liner to sense temperature, pressure, and other tire parameters, and a transponder which is associated with the tire for transmitting data from the tire/wheel to a separate external receiver. In addition, advantages in programming the transponder enable enhanced battery life, thus extending the useful life of the transponder.
It also may be desirable to “read” the tire data as a vehicle passes a standing interrogator. Therefore, a quick and positive identification system for each active tag is highly desirable.
The present invention provides improved cycling arrangements for battery conservation, novel tag identification techniques, and flexibility in the transponder's transmission performance.